This invention relates generally to sheet feeding mechanisms and more particularly to drive means for transporting sheets having wet images thereon comprising drive rollers which do not disturb the wet images by pushing or squeezing the recording liquid into non-image areas thus avoiding print defects.
In prior art sheet handling devices, shingling apparatus, envelope feeders, and the like, friction rollers having high surface friction characteristics relative to the friction between sheets to be separated are generally employed. For one prior art example of a bottom document feeder, a stack of documents are lowered onto a conveyer which strips the bottom document therefrom and positions it to a metering device for individual withdrawal. The metering device has a retard cylinder and an opposing lower feed roller defining an intake nip for grasping the document delivered thereto by the conveyor. The feed roller has a longer traverse than the conveyor so as to enable complete withdrawal of the document from the stack. For increased friction, it is well known to use ribbed feed rollers in such arrangements. In top document feeders, a high friction feed roller is periodically lowered into contact with the top document of a stack of documents and, in cooperation with a retard pad or retard roller, forwards only the top document from the stack. Shingling apparatus for separating and feeding sheets have been in existence for some time, and many of them use rollers which have ribs or flutes generally to provide increased friction. However, none of the prior art sheet transports solve the problem of driving a recording medium containing liquid images which have not dried without the rollers generating a wave front immediately in front of the roller-to-sheet interface and causing the recording liquid to be pushed or squeezed into non-image areas, thus producing print defects.
U.S. Pat. No. 685,370 to Bridgewater discloses a paper feeding pressure roller which may be solid or hollow for more resilience, formed from rubber, and have a serrated periphery. The serrations are in the form of sharply defined teeth, each having two faces of different angular acuteness, so that the teeth point in the direction of rotation.
U.S. Pat. No. 4,715,593 to Godlewski discloses a stack supporting bottom feed mechanism which provides a novel conveying system for bottom feeding from a stack of items and employs the use of a series of aggressive and nonaggressive rollers. The series of aggressive toothed rollers are driven to rotate half turns and the series of nonaggressive smooth rollers are adapted to lift the stack and provide slide areas for easy removal of an item from the bottom of the stack. This system provides an efficient means to singularly bottom feed paper into a printer or the like.
U.S. Pat. No. 4,687,192 to Hunt discloses a sheet feed apparatus which employs a rotable feed wheel used to shingle a stack of paper. The rotable feed wheel is unitarily constructed and its surface which contacts the sheets of paper is toothed so that it produces a lower coefficient of friction between the wheel protrusions and the outermost sheet of paper being shingled than the coefficient of friction between the outermost sheet and its adjacent sheet in the stack.
U.S. Pat. No. 4,511,135 to Huerta et al. discloses a method and apparatus for feeding envelopes singularly and smoothly into a high speed printer or the like. The envelopes are urged forward using a pressure plate angled at 125 degrees in order to present them to a picking station. The frontmost envelopes are shingled using a ferris wheel type roll wave picker separator. After proper alignment of serrated rollers, the envelopes are accurately fed into a print station. The serrated rollers along with the idler rollers enhance the concavity of the foremost envelope in the stack when it is being shingled forward.
U.S. Pat. No. 3,952,183 to Abe discloses a method and apparatus for counting sheets arranged in a stack. An infeed mechanism comprises first and second rollers which frictionally feed the sheets one by one into the apparatus. Toothed rollers called "star wheels" are positioned on the conveyor belts so that their teeth will engage in the trailing end of each sheet that has been transported into a holder plate. The toothed surface of the star wheel affords sufficient friction between itself and the sheet of paper so that the sheets are fed singularly into the counting mechanism.